Stuck Intake Valves and Ethanol in Gasoline
Several of our marine adjuster clients have sent us intake valves having heavy, black deposits under the crowns. The valves we have received to date have been taken from gasoline engines in older yachts that had recently changed over to gasoline containing ethanol. Bent pushrods and bent valves have been reported with heavy engine damage when pistons impacted the valves.
We removed some of the black sludge from under an intake valve crown. We soaked the sludge in ethanol and, after taking the extract down to dryness, we obtained the infrared absorption spectrum. We found that the material is di-iso octyl phthalate.
We ran a series of experiments using straight gasoline and gasoline with 10% ethanol on fiberglass coupons and coupons of filler taken from one of the fuel tanks of the vessel from which the valves had been taken. Shortly before engine failure that vessel had changed over to gasoline having 10% ethanol. The results can be summarized as follows.
With both the straight gasoline and the gasoline having 10% ethanol, analysis by GCMS shows that the fuel's lightest fractions were absorbed into both fiberglass and filler. Noting the very high flammability and volatility of these light organic compounds, the marine adjuster profession needs to be alert to possible outgassing and fire/explosion hazards.
GCMS shows that the gasoline having 10% ethanol picked up four, very heavy molecules from the fiberglass and two from the filler. The molecular weights of these molecules were in the range of 281 to 379. The straight gasoline did not pick up these molecules. After evaporating the straight gasoline we were left with a thin film. Evaporating the samples that had picked up the heavy molecules we were left with heavy, brown sludge. Infrared spectroscopy showed molecular similarities between the sludge, and the material taken from under the intake valve crowns.
This is what we believe is happening.
Polyester resins, gel coats and fillers commonly incorporate phthalates. For a review of the roles of phthalates in boat hull materials see Rockett, T. J. and Rose, V., "The Causes of Boat Hull Blisters", which can be downloaded from http://www.daviscoltd.com/nams/Documents/Blister_Report.html. In even the best resins and layups, a small proportion of these phthalates remain unreacted. There are several water soluble molecules that are found in these materials and they play a central role in blister formation and delamination. Phthalates are only sparingly soluble in water however many are readily dissolved by ethanol.
Whereas gasoline free from ethanol never picks up phthalates, when ethanol was introduced the very small ethanol molecules diffused into the fiberglass, filler and gel coat materials where they dissolved unreacted phthalates. Having been dissolved by smaller molecules, and almost certainly accelerated by osmotic pressure, some portion diffused back to the surface and was dispersed in the gasoline. Based on our GCMS results to date there are some other, presently unidentified, large molecules that were also leached out by the ethanol and similarly transferred into the gasoline.
This internal solution and diffusion back to the surface is the process of leaching. Leaching by water is described in Rockett loc. cit. in connection with blistering.
Since they are in solution, the phthalates and the other heavy dissolved molecules are able to pass through the fuel line filters. When the gasoline with ethanol evaporates in the carburetor, the heavy molecules do not evaporate but come out of solution and are carried along in the air-fuel mix as an aerosol. When the droplets impinge on throttle plates and on the walls of the induction system they can collect as reported by Chuck Fort in Boat US and others.
We do not presently know if, after impingement, the films are immobile, or if they are able to migrate through the induction system towards the intake valves. Some of the molecules that impinge on the hot valve stems and under the crowns decompose to leave carbon powder and ash. Others, such as the phthalates that in general have exceptional high temperature stability, remain intact or undergo only partial decomposition and then act as the binder that holds together the carbon particles and ash as the observed, black sludge.
Should you need to explore this type of failure we suggest you provide us with an intake valve having the sludge buildup and with a coupon cut from the tank. The coupon could be as small as a 1 inch diameter hole saw disk although we would prefer a little larger. The hole saw needs to be degreased prior to use and both the coupon and the valve should be wrapped in a paper towel before being put into a plastic bag so as to avoid transfer of the bag's surface lubricant onto the samples. It would help if we could also receive scrapings from somewhere within the induction system, such as a throttle plate or carburetor throat below the jets. Our chemists will section the coupon and soak a segment in gasoline with 10% ethanol. Samples of the soaked fuel and the as-received fuel will be taken down to dryness and the infrared spectra will be compared with the spectra of the ethanol extract taken from a valve and from within the induction system. As necessary, GCMS chromatograms, will also be compared. You will receive a report indicating what we found. Since the soaking takes a week, expect about a two week delay before you receive results.
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